The presence of magnesium is confimed in the qualitative analysis by the formation of a white crystalline precipitate of :

Options

A. `Mg(HCO_(3))_(2)`
B. `MgNH_(4)PO_(4)`
C. `MgNH_(4)(HCO_(3))_(3)`
D. `MgCO_(3)`

Explanation

To confirm the presence of magnesium in qualitative analysis, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Compounds**: We are given four options: Magnesium Hydrogen Carbonate, Magnesium Ammonium Phosphate, Magnesium Ammonium Bicarbonate, and Magnesium Carbonate. We need to determine which one forms a white crystalline precipitate.

2. **Understand the Confirmatory Test**: The confirmatory test for magnesium involves the reaction of magnesium salts with specific reagents. In this case, we will focus on Magnesium Ammonium Phosphate.

3. **Write the Reaction**: The reaction for the formation of Magnesium Ammonium Phosphate can be represented as:
\[ \text{MgCl}_2 + \text{Na}_2\text{HPO}_4 + \text{NH}_4\text{OH} \rightarrow \text{MgNH}_4\text{PO}_4 \cdot 6\text{H}_2\text{O} \, (\text{white precipitate}) + \text{NaCl} + \text{H}_2\text{O} \]
Here, Magnesium Chloride reacts with Sodium Hydrogen Phosphate and Ammonium Hydroxide to form Magnesium Ammonium Phosphate, which is a white crystalline precipitate.

4. **Analyze the Precipitate**: The precipitate formed in this reaction is Magnesium Ammonium Phosphate, which confirms the presence of magnesium.

5. **Evaluate the Options**: Based on the reaction and the formation of the white precipitate:
- Magnesium Hydrogen Carbonate: Incorrect
- Magnesium Ammonium Phosphate: Correct
- Magnesium Ammonium Bicarbonate: Incorrect
- Magnesium Carbonate: Incorrect

6. **Conclusion**: The correct answer is **Magnesium Ammonium Phosphate**, which confirms the presence of magnesium in qualitative analysis.

### Final Answer:
The presence of magnesium is confirmed by the formation of a white crystalline precipitate of **Magnesium Ammonium Phosphate**.

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